This invention relates to a valve assembly and relates particularly to a valve assembly having an anti-scald pressure balancer. This invention also relates particularly to a valve assembly having a mixing valve for selectively establishing the mix of hot and cold water passing through the valve assembly.
For some years, a pressure balancer is used in a hot/cold water supply system where hot water is supplied through a pressurized facility separately from the pressurized facility which supplies the cold water. This type of system is usually used in large facilities such as hotels, apartment and condominium complexes, gymnasiums, college dormitories and the like. In such large facilities, large numbers of people may be bathing simultaneously, for example by shower, and thereby placing simultaneous hot and cold water demands on the supply of such facilities. In order to insure that sufficient hot water is available for immediate demand, a hot water supply, separate from the cold water supply, is established and is pressurized independently of the cold water supply. Thus, when demands are made by the users of the system, hot and cold water is available immediately.
When water is demanded by a user for showering, the user adjusts the mixing valve to attain a desired temperature of the mixed hot and cold water. If, during the course of showering, the cold water pressure fails or drops significantly, the user is then subjected instantaneously and unexpectedly to the hot water which is operating under the separate pressurizing system. This could result in serious scalding of the user. In addition, if the hot water pressure fails or drops significantly, the user is subjected instantaneously and unexpectedly to the cold water which, while not as potentially harmful to the user's well being as failure of the hot water pressure, could be startling and extremely unpleasant.
In the past, in order to prevent the unexpected reaction to the failure of either the hot water pressure or the cold water pressure in such independently pressurized systems, a pressure balancer has been used to effectively shut off the supply of either hot or cold water upon failure of the pressurized supply of the other.
The pressure balancer also responds to changes in the pressure of the hot and cold water supplies where such changes do not constitute a failure of the pressure but do represent sufficient pressure change to alter the mix of the hot and cold water. In such conditions, the temperature of the mixed hot and cold water, as detected by the user, changes noticeably and, at times, unpleasantly. The pressure balancer responds to such pressure changes by balancing or equalizing the pressure on the hot water side and the cold water side of the balancer which tends to restore the hot and cold water mix level established prior to the above-noted change in the initial pressure level.
In recent years, many States have instituted code provisions which require the installation of such pressure balancers in new residential homes even though residential homes typically do not have separate hot and cold water pressure systems. Nonetheless, this action has added another layer of significance in the utilization of pressure balancers. Within the next several years, it is expected that all States will have such requirements.
Typically, a pressure balancer includes a poppet unit having two poppets where each is formed with hard closure surfaces with one poppet located in a hot water flow path and the other poppet located in a cold water flow path. The flow paths are separated by a diaphragm to which the poppet unit is connected. The diaphragm, which separates the two flow paths, is responsive to changes in the pressure of the hot and cold water passing through the paths and moves the poppet unit and poppets accordingly. When the hot and cold water pressures are equal, the system is balanced and the diaphragm is in a neutral position. When the cold water pressure decreases or fails, the diaphragm moves toward the cold water flow path and pulls or moves the poppets accordingly. As the poppets move, the hard closure surface of the poppet in the hot water flow path moves closer to or into engagement with a hard fixed surface to effectively control flow of the hot water upon a decrease in the cold water pressure or to effectively seal the hot water flow path upon failure of the cold water pressure and thereby prevent scalding of the user of the related shower. The pressure balancer operates in a similar fashion when the hot water pressure decreases or fails and thereby controls the cold water flow or shuts off the cold water accordingly.
While the above-described pressure balancer functions theoretically as described, the practical success of such a pressure balancer is dependent to some extent upon the flow controlling structure of the surfaces, and to another extent upon the sealing ability of the hard closure surfaces of the poppets and the respective hard fixed surfaces. If the integrity of these mating surfaces is poor and they do not seat properly, for example due to poor construction or wear, the sealing ability of the pressure balancer is less than effective and the user of the shower may still be subjected to scalding or to the sudden shock of cold water.
Various organizations which set standards for the operation of plumbing products have recognized the serious consequences of defective performance of pressure balancers and have set standards for minimum allowable leakage during a shut off mode. While new pressure balancers may function in accordance with the standards at the outset, there could be a tendency for failures to occur after some period of use due to wear.
It is important that a pressure balancer be capable of controlling water flow during the pressure changes noted above. Without such control, the diaphragm may not be responsive and thereby fail to react as required. This failure of control typically occurs when the effective opening between the moving hard closure surface of the poppet and the hard fixed surface remains essentially unchanged due to the geometry of the two surfaces. The unchanging opening does not allow the development of increased resistance in the flow path which would normally result from the continuing closure of the opening. This results in no pressure change at the surface of the diaphragm which ceases to move the poppet whereby the pressure balancer fails to perform effectively.
Thus, it is important to provide a pressure balancer which allows for full and continued response to changes in water pressure in order to effectively control the continued balancing performance of the pressure balancer.
In addition to the problems noted above, when a failure occurs in the hot or cold pressurized water systems, a pulsating reaction occurs wherein the hard closure surface repeatedly engages the hard fixed surface. This results in a loud chattering noise which is offensive noise pollution. Further, such repeated engagement tends to wear the sealing surfaces thereby hastening the problems noted above with regard to the integrity of the seal attainable by the pressure balancer.
Thus, there is a need for a valve assembly having a long-life pressure balancer with high integrity which effectively seals the hot and cold water flow paths on demand and which does so with no noticeable noise pollution.
The sensitivity and responsiveness of pressure balancers which use a diaphragm is directly related to the effective area of the diaphragm which is subjected to the pressure changes of the hot and cold water. In past attempts to expand this sensitivity reaction, water from other portions of the flow paths has been directed into chambers behind the end of each poppet which results in the water pressure being applied against the ends of the poppets. In this manner, the effective responsive area to water pressure change has been increased by the area of the ends of the poppets. However, to preclude the leakage of such chambered water along the sides of the poppets and into the flow paths adjacent the poppets, additional sealing means such as compliant O-rings had to be assembled about the periphery of each of the poppets and within cylindrical wells in which the poppets are contained and move. Eventual wear of the O-rings, due to the frictional engagement of the moving O-rings with the walls of wells, could result in the leakage along the sides of the poppets as noted above. This would then decrease the effectiveness of the chambered water pressure on the poppets. In addition, the presence of the O-rings introduced an additional drag in the responsive performance of the pressure balancer. Under such conditions, the pressure balancer had to overcome the resistance of the moving frictional engagement of the O-rings with the well walls in order to perform as required.
Thus, there is a need for a valve assembly having a pressure balancer which is capable of utilizing, long term, the principle of water pressure on the poppet ends to enhance the area responsive to water pressure changes without the negative trade-off of O-ring friction.
Since the poppet includes the hard closure surfaces, the distance of travel of the poppet to engage the hard fixed surfaces, in response to pressure failure of the respective water supplies, becomes critical during the operation of the pressure balancer. Thus, the dimensioning and the tolerancing of the poppet during the manufacture thereof also is extremely critical. Currently, poppet units are composed of several axially aligned pieces which are assembled by various means of securance to provide a unitary product. In the design of the multiple piece poppet, each piece is designed with a dedicated tolerance limit in the axial direction. When the pieces are assembled in an axial configuration to form the poppet unit, the tolerances of all of the pieces are cumulative in the axial direction. Thus, while the piece of the poppet unit which includes one of the hard closing surfaces is made with an acceptable tolerance for locating the surface a desired normal distance from the hard fixed surface, the cumulative effect of assembly of that piece with the other pieces of the poppet may place the closing surface an undesirable "normal" distance from the fixed surface.
Consequently, there is a need for a poppet structure which essentially eliminates concern for the cumulative effect of multiple tolerances.
In current valve assemblies, hot and cold water is passed through the water flow paths, through water seals and through selectively shaped holes in a selectively positionable mixing valve and into a mixing chamber to attain a mixture of the hot and cold water. The mixing valve typically includes a plastic throttling member having a disc-like base with the selectively shaped holes formed therethrough. A stem is formed on the base and extends axially therefrom. A stainless steel plate is formed with the selectively shaped holes and with tabs which extend axially from the side of the plate. The plate is assembled with the base by inserting the tabs into receptacles of the plastic base whereby the integrity of the plastic walls of the receptacles is disturbed. Eventually, if the plate has to be removed and replaced, the wall of the plastic receptacle is so disrupted that the tabs will no longer be retainable with the receptacles.
Thus, there is a need for a valve assembly having facility for assembling the tabs of the stainless steel throttle plate with the receptacles of the plastic base with the ability to remove the tabs therefrom without repeated disruption of the plastic walls of the receptacles.
In the formation of the stem of the plastic throttling member, it would be desirable to form various reliefs during the plastic curing stage to reduce the undesirable effects typically experienced in the curing of thick plastic parts. However, where the appearance of such reliefs is similar to receptacles for other parts which are to be assembled with the stem, assemblers could mistakenly assemble the other parts in the reliefs. This could result in defective operation of the valve assembly.
Thus, there a need for a valve assembly having a plastic stem with reliefs to facilitate the manufacture of the plastic stem while insuring that other parts are not assembled in the reliefs.